The effect of dehydro-L-ascorbic acid (DHA) on L-ascorbic acid oxidase in the rat liver homogenate was observed with Warburg apparatus and the following conclusions were obtained. L-Ascorbic acid (ASA) and DHA were destroyed considerably even in a state of phosphate buffer solution but when liver homogenate was added to solution both ASA and DHA were protected from destruction probably by the protective effect of the protein of the homogenate. DHA had no effect on the destruction of ASA at low concentration of DHA, but it inhibited the destruction of ASA at high concentration. Inhibition of the destruction of ASA by DHA was perhaps due to the effect of DHA on the cytochrome c.